The present invention relates to a double-glazed window structure and in particular, to a structure of a double-glazed window which is formed by attaching an add-on outer window frame to a ready-built inner window frame fixed to a window opening of a finished building.
There may often be cases in which remodeling of a ready-built single-glazed window into a double-glazed window is required in order to increase the sound deadening effect or heat insulation of the window to comply with changes in the use of the building concerned or in the environmental conditions. In such cases, it is an economical way that an add-on outer window frame is attached to the outside of the ready-built window frame, instead of remodeling the window in its entirety. A double-glazed window structure for the purpose is known in which several anchorages with screw sockets (nuts) are provided at the exterior surface of the building wall by being embedded through the outer finishing layer in the body of the building around the window opening at suitable distances from each other, the anchorages being utilized for fastening the add-on outer window frame (see, for example, Japanese Utility Model Disclosure No. 51-62233).
In the above-described structure of the prior art double-glazed window, the add-on outer window frame is attached around the window opening by being fastened to bracket members with bolts and supported by the bracket members which in turn are each fastened to each of the anchorages embedded in the body of the building and, at the same time, the intermediate frame provided at the inboard periphery of the outer window frame is connected at the lower cross-member or sill thereof with screws to the outboard periphery of the ready-built inner window frame.
It is usual that the outward stretch of the window opening, i.e. the distance between the outboard periphery of the ready-built inner window frame and the exterior surface of the wall or the edge of the water nosing, if any, differs considerably according to discrepancy between the centerlines of the wall and the window frame. Satisfactory accuracy is not always ensured in the finishing of the exterior surface of the wall to which the bracket members are to be fastened with the anchorages and the bolts.
Therefore, the above-described double-glazed window structure is disadvantageous due to a requirement for high-precision workmanship in the positioning of the add-on outer window frame and also due to a low efficiency in the construction thereof, because it is a usual practice that an exact base plane is first formed for attaching the bracket members by applying liner materials on to the exterior surface of the wall whereupon the add-on outer window frame is fastened to the bracket members with exact positioning.